Several methods have previously been employed in the processing of glass for the purpose of forming attenuated filaments or fibers for use in reinforcing various thermosetting resins when they are formed into utilitarian objects.
One method involved the steps of melting glass batch in a comparatively large furnace, or glass tank, refining the glass in a refining chamber associated with said glass tank, then forming the glass into spherical bodies or marbles, which are subsequently cooled to room temperature.
These glass marbles were later delivered to a stream feeder, or bushing, which was electrically heated in order to remelt the glass marbles to a viscosity at which streams of glass could be flowed through orifices in the bushing, such flow attenuated into filaments, then converging and collecting same in the form of a strand, on a high speed, rotating mandrel.
The marble method was obviously costly in that it involved special apparatus for handling and feeding the glass marbles, and furthermore required relatively large amounts of electrical energy for remelting the marbles after they had been cooled to room temperature.
More recently, the so-called "direct melt" method has been evolved whereby the glass batch is reduced to a molten state and refined in a suitable glass furnace or glass tank, and the molten glass flowed directly from the glass tank through a forehearth channel, along the bottom of which is disposed a series of streamfeeders or bushings adapted to receive the molten glass directly from the forehearth, with attenuation of the glass into filaments, and collection into a strand, utilizing much the same methods as in the marble system.
The direct melt method was a substantial improvement, in that the marble forming and remelting step was elliminated at a great saving.
Nevertheless, the cost of initially melting the glass raw batch materials, and reducing them to the molten state was still extremely high because, in addition to the heat required to fuse the glass and maintain its molten state, tremendous heat input was also required just to maintain the temperature of the traditional, cathedral-like glass tank, with its massive refractory superstructure, and its cavernous ambient atmosphere above the relatively shallow glass pool. Inefficiancy was compounded by enormous heat losses up the flue as a consequence of the turbulence created by banks of high pressure fuel burners firing directly into the furnace atmosphere.
Exemplary of the size, mass and complexity of glass tanks utilized in conjunction with current direct melt processes, see FIG. 6 of U.S. Pat. No. 3,321,290, issued May 23, 1967, and those portions of the specification describing the furnace.
There has therefore been a long-felt need for some means of melting raw batch glass materials whereby such melting could be quickly and efficiently accomplished in a relatively small, confined fusion zone with the elimination of the inefficient, ponderous glass tanks heretofore utilized in the direct melt operation.